1. Field of the Invention
The present invention relates to a lighting device for a display device which is used for a liquid crystal panel or the like, and a display device using the same.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2004-125964 (FIG. 2) discloses a prior art backlight device for a liquid crystal display. In this backlight device, a plurality of optical films are stacked on each other and opposed to a housing portion of a light source such that light emission from the light source is uniformly irradiated to a display.
A backlight device has to include the plurality of optical sheets without omitting any of the sheets in its assembled state. However, a plurality of optical sheets usually appear to have the same or similar thin sheet shapes, and when they are seen from above in a stacked state, they cannot be discriminated from one another. Therefore, it is difficult to check for the presence of the plurality of optical sheets in the device. Thus, in the backlight device according to the above described prior art, the corner portion of each of the optical sheets is cut off along a straight line, and the cutoff amounts are made to differ in accordance with the respective sheets (the triangular shapes which are cut off from the respective sheets have the same or similar shapes to one another). The sheet with the smallest cutoff amount is on the bottom, and the sheets with larger cutoff amounts are sequentially stacked on top of one another. In this way, the cutoff portions are seen from above during the manufacturing process, so that the lack or absence of one or more of the optical sheets in the assembly is detected.
However, an optical sheet must have a minimum predetermined surface area for maintaining a light control function. Thus, the cutoff portion on each optical sheet must be as small as possible. Accordingly, it is still difficult to see the corner portions cut off along the straight lines and determine the absence of the optical sheets in the manufacturing process.